Using IRQ 2 on an AT is tricky

Thread View: comp.sys.ibm.pc.programmer

1 messages

[T] Back to Threads [V] Tree View [G] Group Articles

1 total messages Started by Russ Nelson Sat, 03 Mar 1990 04:44

#1438

Author: Russ Nelson
Date: Sat, 03 Mar 1990 04:44

17 lines
1359 bytes

I'll bet that you already know that IRQ 2 on the AT bus is mapped to
IRQ 9 on the slave 8259.  You may even realize that the IRQ 9 handler
simply issues an EOI to the slave controller and calls the interrupt
associated with IRQ 2 (INT A).  This ensures that software written for
the PC will work when you use it with IRQ 2.

But what I'll bet you *didn't* realize was that IRQ 9 is enabled at
boot time.  If you have a piece of hardware that generates a spurious
IRQ 9 at initialization time, it will get handled by the default IRQ 2
handler.  This interrupt handler may not do anything useful.  In my
case it crashed my machine.

My solution is to disable interrupts during the time that I'm initializing
the board.
--
--russ (nelson@clutx [.bitnet | .clarkson.edu])  Russ.Nelson@$315.268.6667
Violence never solves problems, it just changes them into more subtle problems

Thread Navigation

This is a paginated view of messages in the thread with full content displayed inline.

Messages are displayed in chronological order, with the original post highlighted in green.

Use pagination controls to navigate through all messages in large threads.

Back to All Threads